The present invention relates to a fluid pressure regulator for use in, for example, an electronically controlled fuel injection system of an internal combustion engine of an automobile.
An example of a conventional fluid pressure regulation system is disclosed in, for example, Japanese Utility Model Application Laid-Open No. 65945/1984 and Japanese Pat. Application Laid-Open No. 132068/1985.
FIGS. 1 and 2 show the fluid pressure regulator of the latter, schematically. In FIG. 1 which shows a fuel injection system having the fluid pressure regulator and FIG. 2 which shows the fluid pressure regulator in cross section, fuel is routed from a fuel tank 1 through a pipe 2 to a fuel pump 3 in which it is pressurized. Then, it is supplied from the fuel pump 3 through a damper 4, a fuel filter 5 and a pipe 6 to a pressure regulator 7 in which a fuel pressure is regulated to a predetermined value. Fuel at the predetermined pressure is supplied through a pipe 6 to a fuel injector 9 of electromagnetic valve type. The fuel injector 9 shown in FIG. 1 responds to an instruction signal from a control unit 10a of a control mechanism 10 for opening the valve for a predetermined time to inject supplied fuel. The injected fuel is mixed with suction air flowing through an intake manifold 11 and then supplied to a combustion chamber 12a of an internal combustion engine 12 for combustion.
Describing the pressure regulator 7 in more detail with reference to FIG. 2, when a pressure of fuel flown from the pipe 6 into a fuel chamber S1 reaches or exceeds a preset value, a valve member 14 mounted on a diaphragm 13 is moved downwardly against a downward force exerted thereon by a spring 15. Therefore, fuel is allowed to flow through an overflow opening 16a given at a lower end of a valve seat 16 and a return pipe 17 to the fuel tank 1. On the other hand, a resiliency of the spring 15 can be controlled in two steps by an electromagnetic mechanism composed of a retainer 18, a rod 19, a spring 20 and a solenoid 21. That is, during a normal engine operation, the solenoid 21 is deenergized by the control mechanism 10 so that the retainer 18 is moved downwardly to press the valve member 14 with a first resiliency of the spring 15. Therefore, pressure in the fuel chamber S1 is set to a first pressure corresponding to the resiliency of the spring 15.
In a case where the engine 12 is stopped and then restarted while it is still hot, there is fuel vapor in the injector 9 and in the fuel pipes and, thus, an amount of fuel to be injected by the injector 9 becomes smaller than desired, resulting in a vapor-lock phenomenon. In order to prevent this phenomenon from occurring, a fuel temperature is detected by a fuel temperature sensor mounted on the injector 9 and switch 10b. When it reaches or exceeds a predetermined temperature, the solenoid 21 is energized for a time preset by a timer 10c to move the retainer upwardly by a predetermined distance to thereby compress the spring 15 so that the valve member 14 is urged by a second resiliency of the spring 15. Therefore, fuel pressure in the fuel chamber S1 is set to a second value corresponding to the second resiliency of the spring 15. Thus, the fuel pressure at the restarting of the engine while the latter is still hot is regulated to the second pressure which is higher than that during the normal engine operation, so that the occurrence of the vapor-lock is prevented to allow the injector 9 to inject a sufficient amount of fuel to burn.
During the operation of the engine mentioned above, a negative pressure introduced through the intake manifold 11 and a pipe 22 to a negative pressure chamber S2 is assumed as being constant for simplicity of explanation. It should be noted, however, that the negative pressure in the chamber S2 depends upon running condition of the engine 12 and, practically, an urging force of the valve member 14 exerted on the valve seat 16 varies accordingly to regulate the pressure in the fuel chamber S1 so that a difference between the intake air pressure in the intake manifold 11 and the fuel pressure in the injector 9 becomes constant.
In the conventional regulator mentioned above, it is necessary to set the second fuel pressure at a very large value to prevent the vapor-lock at the engine restart while it is still hot. This means that a considerable drive force is required to resist or support the second resiliency of the spring 15 which corresponds to the second fuel pressure, resulting in a large size electromagnetic mechanism.
It is usual that the constant fuel pressure value to be regulated by the conventional device is 2 to 3 Kg/cm.sup.2 and so a mounting load of resilient a member which is a product of fuel pressure and a pressure receiving area of the diaphragm is 10 Kg or more. In order to practice this with an electromagnetic device, the latter must be very large in size.